1. Field of the Invention
The present invention pertains to mechanisms and systems for retaining and releasing a missile on a rail launch system.
2. Discussion of the Background
In order to assure accuracy of a missile launcher, it is desirable for a missile launcher to provide a smooth release and induce a minimum of impulse back into the launching platform of an air launched missile. Prior to the fielding of the Army HYDRA 70 Lightweight Launchers, M260 and M261, for the 2.75 Inch Rocket System, the retention mechanisms for tactical launchers fell into three categories.
The first approach was called a material failure detent. For systems that employ this approach, the munition is restrained by a material component that was designed to fail (i.e. break) when the launch motor thrust became higher than the material strength of the detent. Release force is well controlled in this detent mechanism, but the detent is not reusable. The TOW Missile System is an example of this prior art.
The second approach is the spring-friction-override detent. For this approach, the munition is retained by a spring-loaded engagement retainer, a.k.a. the detent. The detent has some angle on the engaging surface, or face. As thrust builds up, the munition overcomes friction of the munition against the engaging surface of the detent. This forces the detent out of the way by overcoming the spring force that holds the retainer in place. Older 2.75 Inch launchers, such as the M158 and the M200 are examples of this prior art. Hellfire missile launchers M272, M279, and M299, such as shown in FIG. 1, are examples of this prior art. The release force is poorly controlled, but the launcher may be used multiple times.
The third approach may be termed the umbilical-pull detent. This is the most complicated detent/retention system. For this approach, the missile is retained in its launch tube by the communication and power plug, commonly called the umbilical. At the moment that the external launch command is transmitted to the missile, the missile thermal batteries are energized. When the missile completes pre-launch checkout, a fire pulse is sent to an explosive squib adjacent to the umbilical. When the squib is fired, the umbilical is retracted.
When the retracted umbilical reaches the end of its motion, a switch is closed and the rocket motor igniter receives a firing pulse over the last external connection to the missile. The missile then is launched out of its tube. During the brief time between umbilical retraction and motor ignition, the missile is held in place by a light spring-friction-detent. The Stinger Surface-to-Air missile is an example of this prior art. This type of detent mechanism is a one-time use only system.
The newest detent approach is called the blast-actuated detent. This approach was developed for the HYDRA 70 M260 and M261 launchers and these launchers are examples of this prior art, shown in FIG. 2. One of the goals of that design was to minimize impulse into the launcher platform during the firing of the rockets. A description of its operation is associated with Prior Art FIG. 2.
FIG. 1 depicts the prior art detent mechanism currently used in the M272, M279, and M299 Hellfire missile launchers. This prior art is the spring-friction-override detent. The detent mechanism is protected from the environment by the detent cover 16. To load a missile, the sides of the middle and aft missile rail shoes are engaged in the grooves 12A on the inside of the missile launcher rail 12. The missile slides aft until the middle shoe on the missile is almost at the detent 10. The handle 24 that is attached to the detent raising cam 14 is rotated counter-clockwise. Rotating the detent raising cam 14 causes the detent 10 to rotate about the detent retainer pivot shaft 18.
As the detent engagement surface 10A is raised, the detent spring 22 is compressed. The handle 24 is held in position while the missile is pushed aft until the middle shoe firmly rests against the aft missile stop 20. The handle 24 is then rotated clockwise and returned to its original position. The detent raising cam 14 also returns to its original position. The detent 10 has engaged the middle shoe of the missile.
The combination of friction between the missile middle shoe, and detent 10 and the spring constant of the detent spring 22 determines the missile release force.
When a Hellfire missile is to be launched, the missile motor is fired. As thrust builds up, the middle shoe pushes against the detent engagement surface 10A of the detent 10. Aided by the angle on the detent engagement surface 10A, the detent 10 rotates clockwise about detent retainer pivot shaft 18. As the detent 10 is forced up, the detent spring 22 is compressed down. When the detent 10 is clear of the missile middle shoe, the missile will then move along the launch rail 12 until the middle and aft shoes drop clear of the rail.
FIG. 2 depicts the prior art detent mechanism currently used in the M260 and M261 varieties of the 2.75 inch diameter Hydra 70 rocket launchers. The detent mechanism holds rockets in the launch tube 26 between the time that the rocket is loaded into the launch tube 26 and the moment the rocket motor is fired. The blast-activated detent mechanism is contained within the detent housing 44. The detent housing 44 is held on the launch tube 26 with strips of aluminum spot welded to the launch tube 26.
When a rocket is loaded, the blast paddle 30 is rotated counter-clockwise about the blast paddle pivot pin 34. As the blast paddle 30 rotates, the blast paddle cam surface 30A rubs on the aft portion of the side contact 40, which is wrapped around the end of the detent housing 44. The side contact 40 is held in place on the detent housing 44 by two rivets 28. The action of rotating the blast paddle 30 pulls the sear 38 in the aft direction against the sear spring 36. The motion of the sear 38 causes the detent 42 to pivot about the detent pivot point 42B. The aft portion of the detent 42 is forced down while the forward end moves up in the vertical plane.
The detent 42 is forced against the detent springs 46. The detent pivot point 42B is a rectangular hole in the retainer plate 49. The retainer plate 49 is held in the detent housing 44 by six rivets 48. The aft motion of the sear 38 removes downward force from the forward end of the side contact 40 causing the contacts to retract out of the launch tube 26. This clears the way for a rocket to be loaded. The blast paddle 30 is rotated until it passes an over center position, which locks the detent 42 into position for loading a rocket.
When a rocket is loaded, it is pushed into the launch tube, 26 until it is in contact with the aft stops 32. To lock the rocket in the launch tube 26, the blast paddle 30 is rotated clockwise about the blast paddle pivot pin 34 so that it will protrude into the aft opening of the launch tube 26. The action causes the sear 38 to move forward, forcing the contact points of the side contact 40 into the rocket contact band. The detent 42 is allowed to pivot about the detent pivot point 42B until the detent engagement groove 42A of the detent 42 engages the detent ring on the rocket nozzle. The detent springs 46 hold the detent 42 in position while it has engaged the rocket nozzle.
Launching the rocket consists of a process that is the opposite of loading the launcher. When the rocket motor receives an electrical firing pulse through the side contact 40, the rocket motor igniter fires and sends hot gases to light the motor grain. The hot gases also exit the rocket nozzle and put an unbalanced gas pressure on the blast paddle 30. The unbalanced pressure causes the blast paddle 30 to rotate counter-clockwise about the blast paddle pivot pin 34, with the blast paddle cam surface 30A sliding over the rub surface of the side contact 40. As the blast paddle 30 rotates, it pulls the sear 38 aft, compressing the sear spring 36.
The motion of the sear 38 allows the side contact 40 to withdraw from the rocket contact band groove. The motion of the sear 38 also causes the detent 42 to rotate about the detent pivot point 42B in the retainer plate 49 and out of the launch tube 26. This disengages detent engagement groove 42A of the detent 42 from the detent ring on the rocket nozzle. The action of the detent 42 compresses the detent springs 46. As the thrust of the rocket motor builds up, the rocket is free to slide down the launch tube 26 only being restrained by friction.